The present invention relates to a method of forming or molding a circuitry by molding a resin on a plurality of bus bars inserted at a small pitch (at small intervals) in a mold, and the present invention also relates to a mold structure used in this molding method.
A circuitry, having bus bars, is used in an internal circuit of an electric part such as a connector. This circuitry is produced by inserting a plurality of bus bars into a mold and then by injecting a resin into the mold to form a resin-molded portion. As a result, the resin-molded portion holds the bus bars in such a manner that the adjacent bus bars are kept out of contact with each other.
FIGS. 4 and 5 show a related method of molding such a circuitry. A mold 1 has a cavity portion 3 in which a plurality of bus bars 2 are held in a juxtaposed manner. Holder pins 4 are provided in the cavity portion 3, and these holder pins 4 hold the plurality of bus bars 2 at small intervals in such a manner that the bus bars will not contact with one another. The holder pins 4 are arranged substantially on a common straight line in a direction of juxtaposition of the bus bars 2.
In this method, the bus bars 2 are juxtaposed in the cavity portion 3 of the mold 1 in such a manner that each bus bar 2 is inserted between the associated holder pins 4, and then the mold is clamped, and then molten resin is injected into the cavity 1 through a gate (not shown). The molten resin thus injected flows in between the bus bars 2, and is solidified to form resin-molded portions 5, and each resin-molded portion 5, formed between the associated adjacent bus bars 2, holds these bus bars 2 out of contact with each other, as shown in FIG. 5.
In the above molding method, however, the holder pins 4 and the bus bars 2 are arranged so densely that the resin can not easily flow in between the bus bars 2, and therefore the resin-molded portions 5 are liable to be formed with insufficient length (short shot). And besides, since the holder pins 4 are arranged such that each of the bus bars 2 is held at two juxtaposed points on a common line perpendicular to an extending direction of the bus bars 2, each holder pin 4 functions as a rotational fulcrum for the associated bus bar 2, so that the bus bars 2 are liable to be turned as indicated by arrows in FIG. 6. This results in a problem that the adjacent bus bars 2 are brought into contact with each other. Furthermore, since the holder pins 4 are arranged on a common line, the holder pins 4 are disposed close to one another as shown in FIG. 7. Therefore, the whole of each holder pin 4, including its base portion 4a, can not be made thick, and therefore the holder pin 4 has a reduced strength, and is liable to be broken.